Nature of Acid in Soft Water in Relation to the Growth of Brown Trout

IN 1937 I made a brief survey of some small lochs in Sutherland, in some of which the water was fairly acid (pH 4·5). I found, as Captain Sawyer1 has done, that the pH of these waters could be changed very rapidly towards neutrality by shaking with air; and I concluded, like him, that the acidity was due mainly, if not entirely, to dissolved carbon dioxide.